Tiger Woods and Lindsey Vonn's first night out together in the Big Apple didn't exactly go without a hitch. After walking the red carpet amid a sea of celebrities for the annual Costume Institute gala at the Metropolitan Museum of Art in New York, the talked-about couple headed downtown for a star-studded afterparty at the Boom Boom Room, held at the top of the Standard Hotel.

Looking stunning in a long white dress with high see-through slits in the front, the blond ski champ, 28, confidently steered her golfer beau, 37, through the formidable crowd. (Leonardo DiCaprio, Anne Hathaway, Amanda Seyfried, Chris Brown, Solange Knowles and Kate Upton were just a few of the boldfaced attendees.)

"Tiger looked uncomfortable," an onlooker at the Boom Boom Room says. The twosome checked out the Manhattan skyline (with a tux-clad Woods embracing Vonn from behind) and then took their seats, where they chatted, drank, held hands and kissed for much the night. At one point in the evening, the once-divorced golfer got up to dance awkwardly, bopping from side to side and grabbing Vonn's butt affectionately as she giggled.

When it was time to go, around 2 a.m., a seemingly tipsy Woods fell while walking up a small flight of stairs -- and didn't move from the spot until Vonn, clenching her teeth and looking embarrassed, helped him up and guided him (swaying a bit as he walked) to the exit, according to a witness.

In their red-carpet debut as a couple, the pair attended the Met gala as guests of Vogue; the magazine dressed both of the athletes, who declined interviews with reporters on the carpet.

"Lindsey and I have been friends for some time, but over the last few months we have become very close and are now dating," Woods wrote when he and Vonn announced their relationship via Facebook last March. He famously split from wife Elin Nordegren back in 2010 following an epic cheating scandal.